Advanced gain shaping for envelope tracking power amplifiers

ABSTRACT

Envelope tracking power amplifiers with advanced gain shaping are provided. In certain implementations, a power amplifier system includes a power amplifier that amplifies a radio frequency (RF) signal and an envelope tracker that controls a voltage level of a supply voltage of the power amplifier based on an envelope of the RF signal. The power amplifier system further includes a gain shaping circuit that generates a gain shaping current that changes with the voltage level of the supply voltage from the envelope tracker. For example, the gain shaping circuit can include an analog look-up table (LUT) mapping a particular voltage level of the supply voltage to a particular current level of gain shaping current. Additionally, the gain shaping circuit biases the power amplifier based on the gain shaping current.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/802,935, filed Feb. 27, 2020 and titled “ADVANCED GAIN SHAPING FORENVELOPE TRACKING POWER AMPLIFIERS,” which claims the benefit ofpriority under 35 U.S.C. § 119 of U.S. Provisional Patent ApplicationNo. 62/866,155, filed Jun. 25, 2019 and titled “ADVANCED GAIN SHAPINGFOR ENVELOPE TRACKING POWER AMPLIFIERS,” and of U.S. Provisional PatentApplication No. 62/814,429, filed Mar. 6, 2019 and titled “ADVANCED GAINSHAPING FOR ENVELOPE TRACKING POWER AMPLIFIERS,” each of which is hereinincorporated by reference in its entirety.

BACKGROUND Technical Field

Embodiments of the invention relate to electronic systems, and inparticular, to radio frequency (RF) electronics.

Description of the Related Technology

Power amplifiers are used in RF communication systems to amplify RFsignals for transmission via antennas.

Examples of RF communication systems with one or more power amplifiersinclude, but are not limited to, mobile phones, tablets, base stations,network access points, customer-premises equipment (CPE), laptops, andwearable electronics. For example, in wireless devices that communicateusing a cellular standard, a wireless local area network (WLAN)standard, and/or any other suitable communication standard, a poweramplifier can be used for RF signal amplification. An RF signal can havea frequency in the range of about 30 kHz to 300 GHz, such as in therange of about 410 MHz to about 7.125 GHz for fifth generation (5G)Frequency Range 1 (FR1) communications.

SUMMARY

In certain embodiments, the present disclosure relates to a poweramplifier system. The power amplifier system includes a power amplifierconfigured to amplify a radio frequency signal, an envelope trackerconfigured to control a voltage level of a supply voltage of the poweramplifier based on an envelope of the radio frequency signal, and a gainshaping circuit configured to generate a gain shaping current based onthe voltage level of the supply voltage from the envelope tracker, andto bias the power amplifier based on the gain shaping current.

In some embodiments, the gain shaping circuit is operable to map aplurality of supply voltage levels of the supply voltage to acorresponding plurality of current levels of the gain shaping current.

In various embodiments, the gain shaping circuit provides a plurality ofdifferent gain expansions for a plurality of different voltage levels ofthe supply voltage.

In a number of embodiments, the gain shaping circuit reduces the gainshaping current in response to an increase in the voltage level of thesupply voltage of the power amplifier.

In several embodiments, the gain shaping circuit includes a plurality ofcurrent steering circuits each configured to control the gain shapingcurrent based on a comparison relating to the voltage level of thesupply voltage. In accordance with various embodiments, the gain shapingcircuit includes a regulator configured to generate a plurality ofreference voltages of different voltage levels, and the plurality ofcurrent steering circuits are each configured to compare the supplyvoltage to a corresponding one of the plurality of reference voltages.According to a number of embodiments, the power amplifier system furtherincludes a regulator configured to generate a common reference voltageand a resistor ladder configured to receive the supply voltage and togenerate a plurality of scaled supply voltages, and the plurality ofcurrent steering circuits are each configured to compare the commonreference voltage to a corresponding one of the plurality of scaledsupply voltages.

In some embodiments, the gain shaping circuit biases at least one stageof the power amplifier. According to several embodiments, the at leastone stage includes a driver stage. In accordance with a number ofembodiments, the power amplifier system further includes an inputmatching network connected between an input terminal and the driverstage, and the gain shaping current is configured to couple a portion ofthe radio frequency signal at the input terminal to a bias input of thedriver stage.

In a number of embodiments, the power amplifier is a class E poweramplifier.

In several embodiments, the gain shaping circuit is further configuredto generate a reference current, and to bias the power amplifier basedon the reference current. According to a number of embodiments, the gainshaping circuit is configured to adjust the reference current to accountfor process variation. In accordance with various embodiments, the gainshaping circuit is configured to adjust the reference current based on afrequency of the radio frequency signal. According to some embodiments,the gain shaping circuit is configured to generate the reference currentwith a temperature compensated slope. In accordance with a number ofembodiments, the gain shaping circuit is configured to bias the poweramplifier based on combining the reference current and the gain shapingcurrent.

In some embodiments, the power amplifier system is implemented in userequipment of a cellular network.

In certain embodiments, the present disclosure relates to a method ofamplification in a radio frequency communication system. The methodincludes amplifying a radio frequency signal using a power amplifier,controlling a voltage level of a supply voltage of the power amplifierbased on an envelope of the radio frequency signal using an envelopetracker, and biasing the power amplifier based on a gain shaping currentusing a gain shaping circuit, including controlling the gain shapingcurrent based on the voltage level of the supply voltage from theenvelope tracker.

In a number of embodiments, the method further includes mapping aplurality of supply voltage levels of the supply voltage to acorresponding plurality of current levels of the gain shaping current.

In several embodiments, the method further includes providing aplurality of different gain expansions for a plurality of differentvoltage levels of the supply voltage.

In some embodiments, the method further includes reducing the gainshaping current in response to an increase in the voltage level of thesupply voltage of the power amplifier.

In various embodiments, controlling the gain shaping current includesindividually selecting one or more of a plurality of current steeringcircuits based on the voltage level of the supply voltage.

In some embodiments, biasing the power amplifier with the gain shapingcurrent includes biasing at least one stage of the power amplifier. Inaccordance with a number of embodiments, the at least one stage includesa driver stage. According to several embodiments, the method furtherincludes providing input matching using an input matching network thatis coupled between an input terminal and the driver stage, and couplinga portion of the radio frequency signal at the input terminal to a biasinput of the driver stage using the gain shaping circuit.

In various embodiments, the method further includes generating areference current using the gain shaping circuit, and further biasingthe power amplifier based on the reference current. According to severalembodiments, the method further includes adjusting the reference currentto account for process variation. In accordance with a number ofembodiments, the method further includes adjusting the reference currentbased on a frequency of the radio frequency signal. According to someembodiments, the method further includes changing the reference currentwith a temperature compensated slope. In accordance with severalembodiments, the method further includes combining the reference currentand the gain shaping current.

In certain embodiments, the present disclosure relates to a mobiledevice. The mobile device includes a power management system includingan envelope tracker configured to control a voltage level of a supplyvoltage based on an envelope of a radio frequency signal, a transceiverconfigured to generate the radio frequency signal, and a front endsystem including a power amplifier configured to amplify the radiofrequency signal, and a gain shaping circuit configured to generate again shaping current based on the voltage level of the supply voltagefrom the envelope tracker, and to bias the power amplifier based on thegain shaping current.

In various embodiments, the gain shaping circuit is operable to map aplurality of supply voltage levels of the supply voltage to acorresponding plurality of current levels of the gain shaping current.

In several embodiments, the gain shaping circuit provides a plurality ofdifferent gain expansions for a plurality of different voltage levels ofthe supply voltage.

In some embodiments, the gain shaping circuit reduces the gain shapingcurrent in response to an increase in the voltage level of the supplyvoltage of the power amplifier.

In various embodiments, the gain shaping circuit includes a plurality ofcurrent steering circuits each configured to control the gain shapingcurrent based on a comparison relating to the voltage level of thesupply voltage. According to a number of embodiments, the gain shapingcircuit includes a regulator configured to generate a plurality ofreference voltages of different voltage levels, and the plurality ofcurrent steering circuits are each configured to compare the supplyvoltage to a corresponding one of the plurality of reference voltages.In accordance with several embodiments, the mobile device furtherincludes a regulator configured to generate a common reference voltageand a resistor ladder configured to receive the supply voltage and togenerate a plurality of scaled supply voltages, and the plurality ofcurrent steering circuits are each configured to compare the commonreference voltage to a corresponding one of the plurality of scaledsupply voltages.

In several embodiments, the gain shaping circuit biases at least onestage of the power amplifier. According to a number of embodiments, theat least one stage includes a driver stage. In accordance with variousembodiments, mobile device further includes an input matching networkconnected between an input terminal and the driver stage, and the gainshaping current is configured to couple a portion of the radio frequencysignal at the input terminal to a bias input of the driver stage.

In some embodiments, the power amplifier is a class E power amplifier.

In various embodiments, the gain shaping circuit is further configuredto generate a reference current, and to bias the power amplifier basedon the reference current. According to a number of embodiments, the gainshaping circuit is configured to adjust the reference current to accountfor process variation. In accordance with several embodiments, the gainshaping circuit is configured to adjust the reference current based on afrequency of the radio frequency signal. According to a number ofembodiments, the gain shaping circuit is configured to generate thereference current with a temperature compensated slope. In accordancewith some embodiments, the gain shaping circuit is configured to biasthe power amplifier based on combining the reference current and thegain shaping current.

In a number of embodiments, the mobile device further includes a batteryoperable to provide a battery voltage to the envelope tracker.

In several embodiments, the transceiver is further configured to providethe envelope tracker with an envelope signal indicating the envelope ofthe radio frequency signal.

In some embodiments, the power amplifier is configured to output anamplified radio frequency signal, and the mobile device further includesan antenna configured to wirelessly transmit the amplified radiofrequency signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of this disclosure will now be described, by way ofnon-limiting example, with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of one example of a communication network.

FIG. 2 is a schematic diagram of a power amplifier system with advancedgain shaping according to one embodiment.

FIG. 3 is a schematic diagram of a power amplifier system with advancedgain shaping according to another embodiment.

FIG. 4 is a schematic diagram of a power amplifier system with advancedgain shaping according to another embodiment.

FIG. 5A is a schematic diagram of one embodiment of a power amplifierbiasing circuit with advanced gain shaping.

FIG. 5B is a graph of gain shaping current versus supply voltage for oneimplementation of the power amplifier biasing circuit of FIG. 5A.

FIG. 6A is a schematic diagram of a current controller according to oneembodiment.

FIG. 6B is a schematic diagram of a current controller according toanother embodiment.

FIG. 7 is a schematic diagram of one embodiment of a mobile device.

FIG. 8 is a schematic diagram of a power amplifier system according toone embodiment.

FIG. 9A is a schematic diagram of one embodiment of a packaged module.

FIG. 9B is a schematic diagram of a cross-section of the packaged moduleof FIG. 9A taken along the lines 9B-9B.

FIG. 10A is a schematic diagram of a cross-section of another embodimentof a packaged module.

FIG. 10B is a perspective view of another embodiment of a packagedmodule.

FIG. 11 is a schematic diagram of one embodiment of a communicationsystem for transmitting RF signals.

FIG. 12A shows a first example of a power amplifier supply voltageversus time.

FIG. 12B shows a second example of a power amplifier supply voltageversus time.

FIG. 13A is one example of a graph of current versus time.

FIG. 13B is another example of a graph of current versus time.

FIG. 13C is one example of a graph of transistor bias source impedanceversus frequency.

FIG. 14A is one example of a graph of amplitude distortion versus outputpower for various implementations of class E power amplifiers.

FIG. 14B is one example of a graph of driver stage base voltage versusoutput power for various implementations of class E power amplifiers.

FIG. 14C is one example of a graph of output stage base voltage versusoutput power for various implementations of class E power amplifiers.

FIG. 14D is one example of current versus frequency for variousimplementations of class E power amplifiers.

FIG. 15A is one example of a graph of normalized amplitude distortionversus output power for a class E power amplifier operating at varioussupply voltage levels.

FIG. 15B is one example of a graph of normalized phase distortion versusoutput power for a class E power amplifier operating at various supplyvoltage levels.

FIG. 16A is another example of a graph of normalized amplitudedistortion versus output power for a class E power amplifier operatingat various supply voltage levels.

FIG. 16B is another example of a graph of normalized phase distortionversus output power for a class E power amplifier operating at varioussupply voltage levels.

FIG. 17A is one example of measurement results of gain versus outputpower for a class E power amplifier operating at various supply voltagelevels.

FIG. 17B is another example of measurement results of gain versus outputpower for a class E power amplifier operating at various supply voltagelevels.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following detailed description of certain embodiments presentsvarious descriptions of specific embodiments. However, the innovationsdescribed herein can be embodied in a multitude of different ways, forexample, as defined and covered by the claims. In this description,reference is made to the drawings where like reference numerals canindicate identical or functionally similar elements. It will beunderstood that elements illustrated in the figures are not necessarilydrawn to scale. Moreover, it will be understood that certain embodimentscan include more elements than illustrated in a drawing and/or a subsetof the elements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

The International Telecommunication Union (ITU) is a specialized agencyof the United Nations (UN) responsible for global issues concerninginformation and communication technologies, including the shared globaluse of radio spectrum.

The 3rd Generation Partnership Project (3GPP) is a collaboration betweengroups of telecommunications standard bodies across the world, such asthe Association of Radio Industries and Businesses (ARIB), theTelecommunications Technology Committee (TTC), the China CommunicationsStandards Association (CCSA), the Alliance for TelecommunicationsIndustry Solutions (ATIS), the Telecommunications Technology Association(TTA), the European Telecommunications Standards Institute (ETSI), andthe Telecommunications Standards Development Society, India (TSDSI).

Working within the scope of the ITU, 3GPP develops and maintainstechnical specifications for a variety of mobile communicationtechnologies, including, for example, second generation (2G) technology(for instance, Global System for Mobile Communications (GSM) andEnhanced Data Rates for GSM Evolution (EDGE)), third generation (3G)technology (for instance, Universal Mobile Telecommunications System(UMTS) and High Speed Packet Access (HSPA)), and fourth generation (4G)technology (for instance, Long Term Evolution (LTE) and LTE-Advanced).

The technical specifications controlled by 3GPP can be expanded andrevised by specification releases, which can span multiple years andspecify a breadth of new features and evolutions.

In one example, 3GPP introduced carrier aggregation (CA) for LTE inRelease 10. Although initially introduced with two downlink carriers,3GPP expanded carrier aggregation in Release 14 to include up to fivedownlink carriers and up to three uplink carriers. Other examples of newfeatures and evolutions provided by 3GPP releases include, but are notlimited to, License Assisted Access (LAA), enhanced LAA (eLAA),Narrowband Internet of things (NB-IOT), Vehicle-to-Everything (V2X), andHigh Power User Equipment (HPUE).

3GPP introduced Phase 1 of fifth generation (5G) technology in Release15, and plans to introduce Phase 2 of 5G technology in Release 16(targeted for 2020). Subsequent 3GPP releases will further evolve andexpand 5G technology. 5G technology is also referred to herein as 5G NewRadio (NR).

5G NR supports or plans to support a variety of features, such ascommunications over millimeter wave spectrum, beamforming capability,high spectral efficiency waveforms, low latency communications, multipleradio numerology, and/or non-orthogonal multiple access (NOMA). Althoughsuch RF functionalities offer flexibility to networks and enhance userdata rates, supporting such features can pose a number of technicalchallenges.

The teachings herein are applicable to a wide variety of communicationsystems, including, but not limited to, communication systems usingadvanced cellular technologies, such as LTE-Advanced, LTE-Advanced Pro,and/or 5G NR.

FIG. 1 is a schematic diagram of one example of a communication network10. The communication network 10 includes a macro cell base station 1, asmall cell base station 3, and various examples of user equipment (UE),including a first mobile device 2 a, a wireless-connected car 2 b, alaptop 2 c, a stationary wireless device 2 d, a wireless-connected train2 e, a second mobile device 2 f, and a third mobile device 2 g.

Although specific examples of base stations and user equipment areillustrated in FIG. 1 , a communication network can include basestations and user equipment of a wide variety of types and/or numbers.

For instance, in the example shown, the communication network 10includes the macro cell base station 1 and the small cell base station3. The small cell base station 3 can operate with relatively lowerpower, shorter range, and/or with fewer concurrent users relative to themacro cell base station 1. The small cell base station 3 can also bereferred to as a femtocell, a picocell, or a microcell. Although thecommunication network 10 is illustrated as including two base stations,the communication network 10 can be implemented to include more or fewerbase stations and/or base stations of other types.

Although various examples of user equipment are shown, the teachingsherein are applicable to a wide variety of user equipment, including,but not limited to, mobile phones, tablets, laptops, IoT devices,wearable electronics, customer premises equipment (CPE),wireless-connected vehicles, wireless relays, and/or a wide variety ofother communication devices. Furthermore, user equipment includes notonly currently available communication devices that operate in acellular network, but also subsequently developed communication devicesthat will be readily implementable with the inventive systems,processes, methods, and devices as described and claimed herein.

The illustrated communication network 10 of FIG. 1 supportscommunications using a variety of cellular technologies, including, forexample, 4G LTE and 5G NR. In certain implementations, the communicationnetwork 10 is further adapted to provide a wireless local area network(WLAN), such as WiFi. Although various examples of communicationtechnologies have been provided, the communication network 10 can beadapted to support a wide variety of communication technologies.

Various communication links of the communication network 10 have beendepicted in FIG. 1 . The communication links can be duplexed in a widevariety of ways, including, for example, using frequency-divisionduplexing (FDD) and/or time-division duplexing (TDD). FDD is a type ofradio frequency communications that uses different frequencies fortransmitting and receiving signals. FDD can provide a number ofadvantages, such as high data rates and low latency. In contrast, TDD isa type of radio frequency communications that uses about the samefrequency for transmitting and receiving signals, and in which transmitand receive communications are switched in time. TDD can provide anumber of advantages, such as efficient use of spectrum and variableallocation of throughput between transmit and receive directions.

In certain implementations, user equipment can communicate with a basestation using one or more of 4G LTE, 5G NR, and WiFi technologies. Incertain implementations, enhanced license assisted access (eLAA) is usedto aggregate one or more licensed frequency carriers (for instance,licensed 4G LTE and/or 5G NR frequencies), with one or more unlicensedcarriers (for instance, unlicensed WiFi frequencies).

As shown in FIG. 1 , the communication links include not onlycommunication links between UE and base stations, but also UE to UEcommunications and base station to base station communications. Forexample, the communication network 10 can be implemented to supportself-fronthaul and/or self-backhaul (for instance, as between mobiledevice 2 g and mobile device 2 f).

The communication links can operate over a wide variety of frequencies.In certain implementations, communications are supported using 5G NRtechnology over one or more frequency bands that are less than 6Gigahertz (GHz) and/or over one or more frequency bands that are greaterthan 6 GHz. For example, the communication links can serve FrequencyRange 1 (FR1), Frequency Range 2 (FR2), or a combination thereof. In oneembodiment, one or more of the mobile devices support a HPUE power classspecification.

In certain implementations, a base station and/or user equipmentcommunicates using beamforming. For example, beamforming can be used tofocus signal strength to overcome path losses, such as high lossassociated with communicating over high signal frequencies. In certainembodiments, user equipment, such as one or more mobile phones,communicate using beamforming on millimeter wave frequency bands in therange of 30 GHz to 300 GHz and/or upper centimeter wave frequencies inthe range of 6 GHz to 30 GHz, or more particularly, 24 GHz to 30 GHz.

Different users of the communication network 10 can share availablenetwork resources, such as available frequency spectrum, in a widevariety of ways.

In one example, frequency division multiple access (FDMA) is used todivide a frequency band into multiple frequency carriers. Additionally,one or more carriers are allocated to a particular user. Examples ofFDMA include, but are not limited to, single carrier FDMA (SC-FDMA) andorthogonal FDMA (OFDMA). OFDMA is a multicarrier technology thatsubdivides the available bandwidth into multiple mutually orthogonalnarrowband subcarriers, which can be separately assigned to differentusers.

Other examples of shared access include, but are not limited to, timedivision multiple access (TDMA) in which a user is allocated particulartime slots for using a frequency resource, code division multiple access(CDMA) in which a frequency resource is shared amongst different usersby assigning each user a unique code, space-divisional multiple access(SDMA) in which beamforming is used to provide shared access by spatialdivision, and non-orthogonal multiple access (NOMA) in which the powerdomain is used for multiple access. For example, NOMA can be used toserve multiple users at the same frequency, time, and/or code, but withdifferent power levels.

Enhanced mobile broadband (eMBB) refers to technology for growing systemcapacity of LTE networks. For example, eMBB can refer to communicationswith a peak data rate of at least 10 Gbps and a minimum of 100 Mbps foreach user. Ultra-reliable low latency communications (uRLLC) refers totechnology for communication with very low latency, for instance, lessthan 2 milliseconds. uRLLC can be used for mission-criticalcommunications such as for autonomous driving and/or remote surgeryapplications. Massive machine-type communications (mMTC) refers to lowcost and low data rate communications associated with wirelessconnections to everyday objects, such as those associated with Internetof Things (IoT) applications.

The communication network 10 of FIG. 1 can be used to support a widevariety of advanced communication features, including, but not limitedto, eMBB, uRLLC, and/or mMTC.

Advanced Gain Shaping for Envelope Tracking Power Amplifiers

A power amplifier is used to amplify a radio frequency (RF) signal fortransmission on an antenna of an RF communication system, such as amobile device. To extend battery life and/or to reduce heat dissipationof the RF communication system, it is desirable for the power amplifierto operate with high efficiency.

One technique for improving efficiency of a power amplifier is envelopetracking (ET), in which a supply voltage (V_(CC)) of the power amplifieris controlled in relation to the envelope of the RF signal. Thus, when avoltage level of the envelope of the RF signal increases the voltagelevel of the power amplifier's supply voltage is increased. Likewise,when the voltage level of the envelope of the RF signal decreases thevoltage level of the power amplifier's supply voltage is decreased toreduce power consumption.

Peak power added efficiency (PAE) of a power amplifier typically occursrelative close to saturated output power (Psat), which is a highlycompressed operating point. For a power amplifier that operates withenvelope tracking, the power amplifier operates at less than the 1 dBcompression point when V_(CC) is equal to a root mean square voltage(V_(RMS)). In one example, operation below the 1 dB compression pointoccurs frequently for an envelope tracking system using an isogain tableto map an envelope signal to a shaped envelope signal so as to maintaina substantially constant gain across an envelope signal range. PAE of apower amplifier at such operating points is much lower than peak PAE.

To enhance PAE, the power amplifier can be biased such that gainexpansion at V_(RMS) is increased. However, providing gain expansion inthis manner can degrade performance at low V_(CC) levels and/or providetoo much gain expansion at high V_(CC) levels. This in turn canintroduce undesirable memory effects, degrade linearity, and/ordeteriorate receive band specifications, such as desense.

Although a gain boosting circuit can be included to adjust gain shape, again boosting circuit may also degrade linearity.

Advanced gain shaping for envelope tracking power amplifiers isdisclosed herein. In certain implementations, an RF communication systemincludes a power amplifier that amplifies an RF signal and an envelopetracker that controls a voltage level of a supply voltage (V_(CC)) ofthe power amplifier based on an envelope of the RF signal. The RFcommunication system further includes a gain shaping circuit thatgenerates a gain shaping current (I_(ADS)) that changes with the voltagelevel of the supply voltage from the envelope tracker. For example, thegain shaping circuit can include an analog look-up table (LUT) mapping aparticular voltage level of V_(CC) to a particular current level ofI_(ADS). Additionally, the gain shaping circuit biases the poweramplifier based on the gain shaping current.

By implementing the RF communication system in this manner, flexibilityis provided for adjusting gain expansion at different levels of V_(CC).For example, when V_(CC) is about equal to V_(RMS), sharper gaincompression and higher gain expansion can be provided. Additionally,when V_(CC) is equal to a minimum or lowest supply voltage (V_(LOW)), aflat landing zone with low gain distortion (AM/AM) can be provided.Furthermore, when V_(CC) is equal to a maximum or highest supply voltage(V_(HIGH)), low gain expansion can be provided.

By providing different combinations of gain profiles for differentvoltage levels of V_(CC), PAE of a power amplifier can be enhanced, forinstance, by 2% or more. Furthermore, such PAE enhancement can beprovided while maintaining linearity performance. Thus, advanced gainshaping can be used to achieve both good PAE and linearity. In contrast,other approaches suffer from undesirable tradeoffs between efficiencyand linearity.

In certain implementations, the gain shaping circuit includes a currentcontroller implemented on a semiconductor chip, such as a silicon (Si)chip. Additionally, the current controller generates I_(ADS) to changebased on frequency band, for instance, to cover any suitable frequencyrange, including, but not limited to, 450 MHz to 7 GHz, or moreparticularly, 650 MHz to 915 MHz.

In certain implementations, the bias to the power amplifier is generatedbased on both I_(ADS) and a reference current (I_(REF)). Generating thepower amplifier's bias in this manner provides a number of advantages.In a first example, I_(REF) is adjustable (for instance, can be trimmedor otherwise adjusted after manufacture) to reduce process variation.Thus, advanced gain shaping can be implemented to reduce or eliminateprocess variation, thereby providing precise control of bias current. Ina second example, I_(REF) is adjustable for different frequency bands tocover high fractional bandwidth (for instance, 31.9% or more). In athird example, I_(REF) versus V_(CC) LUT is created, thereby defininggain shaping at each V_(CC) level and providing a fast response time. Ina fourth example, I_(REF) provides flexibility to change the gainexpansion, for instance, to fine tune the gain shape. In a fifthexample, I_(REF) is implemented with a temperature compensation slope,thereby compensating gain variation due to temperature.

The power amplifier can be biased based on I_(ADS) in any suitable way.In one example, one or more stages of a power amplifier (including, butnot limited to, a driver stage and/or output stage) is biased based onI_(ADS).

FIG. 2 is a schematic diagram of a power amplifier system 90 withadvanced gain shaping according to one embodiment. The power amplifiersystem 90 includes a power amplifier 81, an envelope tracker 82, and again shaping circuit 83 implemented to provide advanced gain shaping inaccordance with the teachings herein.

In the illustrated embodiment, the power amplifier 81 amplifies an RFinput signal RF_(IN) to generate an RF output signal RF_(OUT). The poweramplifier 81 receives power from a supply voltage V_(CC) that iscontrolled by the envelope tracker 82.

The envelope tracker 82 receives an envelope signal ENVELOPEcorresponding to an envelope of the RF input signal RF_(IN) amplified bythe power amplifier 81. The envelope tracker 82 is powered by a batteryvoltage V_(BATT), and controls the voltage level of the supply voltageV_(CC) based on the envelope signal ENVELOPE.

The gain shaping circuit 83 biases the power amplifier 81 based on again shaping current I_(ADS) that changes based on the voltage level ofthe supply voltage V_(CC) from the envelope tracker 82. For example, thegain shaping circuit 83 can include an analog look-up table (LUT)mapping a particular voltage level of V_(CC) to a particular currentlevel of I_(ADS).

By implementing the RF communication system 90 in this manner,flexibility is provided for adjusting gain expansion at different levelsof V_(CC). By providing different combinations of gain profiles fordifferent voltage levels of V_(CC), PAE of the power amplifier 81 can beenhanced, for instance, by 2% or more. Furthermore, such PAE enhancementcan be provided while maintaining linearity performance. Thus, advancedgain shaping can be used to achieve both good PAE and linearity.

In the illustrated embodiment, the gain shaping current I_(ADS) isprovided to a bias input of the power amplifier 81. In certainimplementations, the gain shaping circuit 83 includes a currentcontroller that generates the gain shaping current I_(ADS), and a poweramplifier biasing circuit that processes the gain shaping currentI_(ADS) to control the bias of the power amplifier 81. In one example,the power amplifier biasing circuit combines the gain shaping currentI_(ADS) with a reference current from the current controller to generatethe bias of the power amplifier 81.

FIG. 3 is a schematic diagram of a power amplifier system 100 withadvanced gain shaping according to another embodiment. The poweramplifier system 100 includes an envelope tracker 82, a first poweramplifier stage 91, a second power amplifier stage 92, and a gainshaping circuit 93 implemented to provide advanced gain shaping inaccordance with the teachings herein. The gain shaping circuit 93includes a current controller 95 and a first power amplifier biasingcircuit 97 that generates a first bias PA1_BIAS for the first poweramplifier stage 91. As shown in FIG. 3 , the power amplifier system 100further includes a second power amplifier biasing circuit 98 thatgenerates a second bias PA2_BIAS for the second power amplifier stage92.

In the illustrated embodiment, the current controller 95 receives thepower amplifier supply voltage V_(CC) from the envelope tracker 82, andgenerates a reference current I_(REF1) and a gain shaping currentI_(ADS). Additionally, the first power amplifier biasing circuit 97generates a first bias PA1_BIAS of the first power amplifier stage 91based on the reference current I_(REF1) and the gain shaping currentI_(ADS). In certain implementations, the first power amplifier biasingcircuit 97 combines the reference current I_(REF1) and the gain shapingcurrent I_(ADS) to generate the first bias PA1_BIAS.

In certain implementations, the current controller 95 is fabricated on afirst semiconductor chip (for instance, a Si chip), while the firstpower amplifier biasing circuit 97, the second power amplifier biasingcircuit 98, the first power amplifier stage 91, and the second poweramplifier stage 92 are fabricated on a second semiconductor chip (forinstance, a compound semiconductor chip, such as a GaAs or GaN chip).

FIG. 4 is a schematic diagram of a power amplifier system 110 withadvanced gain shaping according to another embodiment. The poweramplifier system 110 includes an envelope tracker 82, a first stagebipolar transistor Q1, a second stage bipolar transistor Q2, an inputmatching network 101, an interstage capacitor 102, and a gain shapingcircuit 103 implemented to provide advanced gain shaping in accordancewith the teachings herein. The gain shaping circuit 103 includes acurrent controller 95 and a first power amplifier biasing circuit 107that generates a first bias PA1_BIAS for the first stage bipolartransistor Q1. As shown in FIG. 4 , the power amplifier system 110further includes a second power amplifier biasing circuit 98 thatgenerates a second bias PA2_BIAS for the second stage bipolar transistorQ2.

The gain shaping circuit 103 of FIG. 4 is similar to the gain shapingcircuit 93 of FIG. 3 , except that the gain shaping circuit 103 of FIG.4 is also coupled to an RF input terminal RF_IN connected to an input tothe input matching network 101. Additionally, the gain shaping circuit103 provides the first bias PA1_BIAS to a base of the input stagebipolar transistor Q1 at a node that is connected to an output of theinput matching network 101.

With continuing reference to FIG. 4 , the first power amplifier biasingcircuit 107 receives an RF input signal at the RF input terminal RF_IN,and uses the RF input signal to modulate the base of the input stagebipolar transistor Q1. Thus, the input stage bipolar transistor Q1 isalso biased based on the RF input signal using a feedforward path, inthis embodiment. In particular a base bias voltage of the input stagebipolar transistor Q1 is raised when the RF signal level increases, andlowered when the RF signal level decreases.

FIG. 5A is a schematic diagram of one embodiment of a power amplifierbiasing circuit 180 with advanced gain shaping. The power amplifierbiasing circuit 180 illustrates one embodiment of the first poweramplifier biasing circuit 107 of FIG. 4 . Although one embodiment of apower amplifier biasing circuit is shown, the teachings herein areapplicable to power amplifier biasing circuits implemented in a widevariety of ways. Accordingly, other implementations are possible.

In the illustrated embodiment, the power amplifier biasing circuit 180includes a gain shaping bipolar transistor 151, a gain shaping enableFET 152, a gain shaping biasing resistor 153, a power control circuit154, a gain shaping current resistor 155, a reference current resistor156, a gain shaping current load 157, a reference current load 158, anda signal feed capacitor 167.

As shown in FIG. 5A, the power control circuit 154 includes powercontrol FETs 172 a, 172 b, . . . 172 n that receive power controlsignals PCTL<a>, PCTL<b>, . . . PCTL<n>, respectively. Additionally, thepower control circuit 154 further includes power control bipolartransistors 171 a, 171 b, . . . 171 n and power control resistors 173 a,173 b, . . . 173 n.

The power amplifier biasing circuit 180 receives a gain shaping currentI_(ADS) that changes with the voltage level of the supply voltage froman envelope tracker. For example, the gain shaping current I_(ADS) canbe generated by a current controller that includes a LUT mapping avoltage level of the supply voltage to the gain shaping current I_(ADS).The power amplifier biasing circuit 180 also receives a referencecurrent I_(REF1), which can also be generated by the current controller.

As shown in FIG. 5A, the gain shaping current load 157 includes a firstdiode-connected bipolar transistor 177 a and a second diode-connectedbipolar transistor 177 b electrically connected in series and with oneanother and biased by the gain shaping current I_(ADS). Additionally,the reference current load 158 includes a first diode-connected bipolartransistor 178 a and a second diode-connected bipolar transistor 178 belectrically connected in series and with one another and biased by thereference current I_(REF1).

The gate of the gain shaping enable FET 152 is controlled by an enablesignal EN_ADS for selectively enabling gain shaping. When the gainshaping enable FET 152 is enabled, the gain shaping bipolar transistor151 is biased such that the current through the gain shaping bipolartransistor 151 changes in relation to the gain shaping current I_(ADS).As shown in FIG. 5A, the gain shaping bipolar transistor 151 and thegain shaping biasing resistor 153 are connected in series between thereference voltage V_(REF) and the power amplifier bias PA1_BIAS.

With continuing reference to FIG. 5A, the power control signals PCTL<a>,PCTL<b>, . . . PCTL<n> can be used to selectively enable one or more ofthe power control FETs 172 a, 172 b, . . . 172 n. When a particular FETis enabled, the base of a corresponding one of the power control bipolartransistors 171 a, 171 b, . . . 171 n is biased such that the currentthrough the transistor changes in relation to the reference currentI_(REF1). As shown in FIG. 5A, each of the power control bipolartransistors 171 a, 171 b, . . . 171 n are connected in series with acorresponding one of the power control resistors 173 a, 173 b, . . . 173n to form a group of series transistor/resistor circuit branches.Additionally, the series transistor/resistor branches are connected inparallel with one another between the reference voltage V_(REF) and thepower amplifier bias PA1_BIAS.

Thus, the current provided at the power amplifier bias PA1_BIAS can becontrolled based on the gain shaping current I_(ADS) and the referencecurrent I_(REF1). Furthermore, the power control signals PCTL<a>,PCTL<b>, . . . PCTL<n> can be used to scale the component of the poweramplifier bias PA1_BIAS that changes based on the reference currentI_(REF1).

In the illustrated embodiment, the RF input terminal RF_IN is coupled tothe power amplifier bias terminal PA1_BIAS through the signal feedcapacitor 167 and the gain shaping biasing resistor 153. Thus, a path isprovided for coupling a portion of the RF signal present at the RF inputterminal RF_IN to the power amplifier bias PA1_BIAS.

FIG. 5B is a graph of gain shaping current versus supply voltage for oneimplementation of the power amplifier biasing circuit 180 of FIG. 5A.The graph illustrates one implementation of an I_(ADS) versus V_(CC)profile for a gain shaping circuit implemented in accordance with theteachings herein. Although one example I_(ADS) versus V_(CC) profile isshown, other implementations are possible.

In the example of FIG. 5B, the gain shaping current I_(ADS) is adjustedfrom 0 uA to 200 uA based on a Q1 gain table. Additionally, poweramplifier bias PA1_BIAS is controlled based on the gain shaping currentI_(ADS) and the reference current I_(REF1), which is maintained turnedON while the gain shaping circuit is powered and enabled.

Implementing the gain shaping circuit in this manner provides a numberof advantages, including, but not limited to, flatter landing zone, lessgain expansion at high V_(CC), and/or flexibility for adjusting gainshape for different V_(CC). Furthermore, widening a dynamic range ofV_(CC) LUT permits a more aggressive gain shaping over V_(CC).

FIG. 6A is a schematic diagram of a current controller 310 according toone embodiment. The current controller 310 includes first comparisonFETs 301 a, 301 b, . . . 301 n, second comparison FETs 302 a, 302 b, . .. 302 n, a first current source 303, a second current source 304, acurrent mirror 305, a voltage divider 306, and a regulator 307. Althoughone embodiment of a current controller is shown, the teachings hereinare applicable to current controllers implemented in a wide variety ofways.

The current controller 310 is used to generate a gain shaping currentI_(ADS) for a power amplifier biasing circuit that changes in relationto a voltage level of a supply voltage V_(CC) from an envelope tracker.Although not shown in FIG. 6A, the current controller 310 can alsoinclude a current source for generating a reference current I_(REF1) forthe power amplifier biasing circuit.

In the illustrated embodiment, the voltage divider 306 includes a firstresistor 308 a and a second resistor 308 b that are connected as avoltage divider. Thus, the voltage divider 306 generates a dividedvoltage V_(DIV) (for instance, half the supply voltage from the envelopetracker, or V_(CC)/2).

As shown in FIG. 6A, the divided voltage V_(DIV) is provided to each ofthe first comparison FETs 301 a, 301 b, . . . 301 n. Additionally, theregulator 307 generates multiple regulated voltages V_(REGA), V_(REGB),. . . V_(REGN) of different voltage levels. Furthermore, the regulatedvoltages V_(REGA), V_(REGB), . . . V_(REGN) are provided to the secondcomparison FETs 302 a, 302 b, . . . 302 n, respectively.

The illustrated comparison FETs operate as a current steering circuitthat steers a comparison current I_(CMP) away from the fixed currentI_(FIXED) generated by the first current source 303.

Thus, the amount of current sinking in I_(ADS) is reduced when V_(CC)increases. For example, as V_(CC) increases (for instance, half ofV_(CC) is larger than the reference to be compared with), current stepsI_(A), I_(B), . . . I_(N) are taken in sequence.

In one example, I_(FIXED) is 200 μA and six equally sized currentcomparators are provided, such that about 33 μA is taken from the 200 μAas each comparator is activated in sequence. When V_(CC) reaches a topof the voltage operating range (for instance 5V), all the taps will beactive and steering their currents from the fixed 200 μA, therebycontrolling I_(ADS) to about 0 μA. Although one example of currentsteering thresholds and values has been described, the teachings hereinare applicable to gain shaping circuits implemented in a wide variety ofways. Accordingly, other implementations are possible.

FIG. 6B is a schematic diagram of a current controller 320 according toanother embodiment. The current controller 320 includes first comparisonFETs 301 a, 301 b, . . . 301 n, second comparison FETs 302 a, 302 b, . .. 302 n, a first current source 303, a second current source 304, acurrent mirror 305, a voltage divider 316, and a regulator 317. Althoughone embodiment of a current controller is shown, the teachings hereinare applicable to current controllers implemented in a wide variety ofways.

In comparison to the current controller 310 of FIG. 3A that usesmultiple regulated voltages V_(REGA), V_(REGB), . . . V_(REGN) forcurrent comparisons, the current controller 320 of FIG. 6B uses a commonor shared regulated voltage V_(REG) for comparisons. For example, abandgap voltage can be used directly as a reference voltage for each ofthe taps of the current steering circuits. Additionally, the voltagedivider 316 is implemented to generate different ratios of V_(CC) thatare compared to the regulated voltage V_(REG).

As shown in FIG. 6B, the voltage divider 316 includes a stack ofresistors 318 a, 318 b, 318 c, . . . 318 n.

In certain implementations, the topmost resistor in the stack ofresistors has a resistance R_upper, the lowermost resistor in the stackof resistors has a resistance R_lower, and the resistors between thetopmost resistor and the lowermost resistor have a resistance R_inner.For example, in a case with a stack of 8 resistors, the topmost resistorcan have a resistance R_upper, the lowermost resistor can have aresistance R_lower, and the six inner resistors can have a resistanceR_inner. Additionally, R_upper and R_lower are used to adjust a rangedesired for voltage sensing and comparison (for instance, 2V<V_(CC)<5V).

In one implementation, a total resistance is 205 kΩ (R_inner=7.5 kΩ,R_upper=105 kΩ, and R_lower=52.5 kΩ), with a unit resistor size of(W×L=1 μm×6.6 μm) and a current consumption of about 24 μA for V_(CC) ofabout 5 V. However, other implementations are possible.

FIG. 7 is a schematic diagram of one embodiment of a mobile device 800.The mobile device 800 includes a baseband system 801, a transceiver 802,a front end system 803, antennas 804, a power management system 805, amemory 806, a user interface 807, and a battery 808. The mobile device800 can be implemented in accordance with any of the embodiments herein.

The mobile device 800 can be used communicate using a wide variety ofcommunications technologies, including, but not limited to, 2G, 3G, 4G(including LTE, LTE-Advanced, and LTE-Advanced Pro), 5G NR, WLAN (forinstance, Wi-Fi), WPAN (for instance, Bluetooth and ZigBee), WMAN (forinstance, WiMax), and/or GPS technologies.

The transceiver 802 generates RF signals for transmission and processesincoming RF signals received from the antennas 804. It will beunderstood that various functionalities associated with the transmissionand receiving of RF signals can be achieved by one or more componentsthat are collectively represented in FIG. 7 as the transceiver 802. Inone example, separate components (for instance, separate circuits ordies) can be provided for handling certain types of RF signals.

The front end system 803 aids is conditioning signals transmitted toand/or received from the antennas 804. In the illustrated embodiment,the front end system 803 includes antenna tuning circuitry 810, poweramplifiers (PAs) 811, low noise amplifiers (LNAs) 812, filters 813,switches 814, and signal splitting/combining circuitry 815. However,other implementations are possible.

For example, the front end system 803 can provide a number offunctionalities, including, but not limited to, amplifying signals fortransmission, amplifying received signals, filtering signals, switchingbetween different bands, switching between different power modes,switching between transmission and receiving modes, duplexing ofsignals, multiplexing of signals (for instance, diplexing ortriplexing), or some combination thereof.

In certain implementations, the mobile device 800 supports carrieraggregation, thereby providing flexibility to increase peak data rates.Carrier aggregation can be used for both Frequency Division Duplexing(FDD) and Time Division Duplexing (TDD), and may be used to aggregate aplurality of carriers or channels. Carrier aggregation includescontiguous aggregation, in which contiguous carriers within the sameoperating frequency band are aggregated. Carrier aggregation can also benon-contiguous, and can include carriers separated in frequency within acommon band or in different bands.

The antennas 804 can include antennas used for a wide variety of typesof communications. For example, the antennas 804 can include antennasfor transmitting and/or receiving signals associated with a wide varietyof frequencies and communications standards.

In certain implementations, the antennas 804 support MIMO communicationsand/or switched diversity communications. For example, MIMOcommunications use multiple antennas for communicating multiple datastreams over a single radio frequency channel. MIMO communicationsbenefit from higher signal to noise ratio, improved coding, and/orreduced signal interference due to spatial multiplexing differences ofthe radio environment. Switched diversity refers to communications inwhich a particular antenna is selected for operation at a particulartime. For example, a switch can be used to select a particular antennafrom a group of antennas based on a variety of factors, such as anobserved bit error rate and/or a signal strength indicator.

The mobile device 800 can operate with beamforming in certainimplementations. For example, the front end system 803 can includeamplifiers having controllable gain and phase shifters havingcontrollable phase to provide beam formation and directivity fortransmission and/or reception of signals using the antennas 804. Forexample, in the context of signal transmission, the amplitude and phasesof the transmit signals provided to the antennas 804 are controlled suchthat radiated signals from the antennas 804 combine using constructiveand destructive interference to generate an aggregate transmit signalexhibiting beam-like qualities with more signal strength propagating ina given direction. In the context of signal reception, the amplitude andphases are controlled such that more signal energy is received when thesignal is arriving to the antennas 804 from a particular direction. Incertain implementations, the antennas 804 include one or more arrays ofantenna elements to enhance beamforming.

The baseband system 801 is coupled to the user interface 807 tofacilitate processing of various user input and output (I/O), such asvoice and data. The baseband system 801 provides the transceiver 802with digital representations of transmit signals, which the transceiver802 processes to generate RF signals for transmission. The basebandsystem 801 also processes digital representations of received signalsprovided by the transceiver 802. As shown in FIG. 7 , the basebandsystem 801 is coupled to the memory 806 of facilitate operation of themobile device 800.

The memory 806 can be used for a wide variety of purposes, such asstoring data and/or instructions to facilitate the operation of themobile device 800 and/or to provide storage of user information.

The power management system 805 provides a number of power managementfunctions of the mobile device 800. In certain implementations, thepower management system 805 includes a PA supply control circuit thatcontrols the supply voltages of the power amplifiers 811. For example,the power management system 805 can be configured to change the supplyvoltage(s) provided to one or more of the power amplifiers 811 toimprove efficiency, such as power added efficiency (PAE).

As shown in FIG. 7 , the power management system 805 receives a batteryvoltage from the battery 808. The battery 808 can be any suitablebattery for use in the mobile device 800, including, for example, alithium-ion battery.

FIG. 8 is a schematic diagram of a power amplifier system 840 accordingto one embodiment. The illustrated power amplifier system 840 includes abaseband processor 821, a transmitter 822, a power amplifier (PA) 823, adirectional coupler 824, front-end circuitry 825, an antenna 826, a PAbias control circuit 827, and a PA supply control circuit 828. Theillustrated transmitter 822 includes an I/Q modulator 837, a mixer 838,and an analog-to-digital converter (ADC) 839. In certainimplementations, the transmitter 822 is included in a transceiver suchthat both transmit and receive functionality is provided. The poweramplifier system 840 can be implemented in accordance with any of theembodiments herein.

The baseband processor 821 can be used to generate an in-phase (I)signal and a quadrature-phase (Q) signal, which can be used to representa sinusoidal wave or signal of a desired amplitude, frequency, andphase. For example, the I signal can be used to represent an in-phasecomponent of the sinusoidal wave and the Q signal can be used torepresent a quadrature-phase component of the sinusoidal wave, which canbe an equivalent representation of the sinusoidal wave. In certainimplementations, the I and Q signals can be provided to the I/Qmodulator 837 in a digital format. The baseband processor 821 can be anysuitable processor configured to process a baseband signal. Forinstance, the baseband processor 821 can include a digital signalprocessor, a microprocessor, a programmable core, or any combinationthereof. Moreover, in some implementations, two or more basebandprocessors 821 can be included in the power amplifier system 840.

The I/Q modulator 837 can be configured to receive the I and Q signalsfrom the baseband processor 821 and to process the I and Q signals togenerate an RF signal. For example, the I/Q modulator 837 can includedigital-to-analog converters (DACs) configured to convert the I and Qsignals into an analog format, mixers for upconverting the I and Qsignals to RF, and a signal combiner for combining the upconverted I andQ signals into an RF signal suitable for amplification by the poweramplifier 823. In certain implementations, the I/Q modulator 837 caninclude one or more filters configured to filter frequency content ofsignals processed therein.

The power amplifier 823 can receive the RF signal from the I/Q modulator837, and when enabled can provide an amplified RF signal to the antenna826 via the front-end circuitry 825.

The front-end circuitry 825 can be implemented in a wide variety ofways. In one example, the front-end circuitry 825 includes one or moreswitches, filters, duplexers, multiplexers, and/or other components. Inanother example, the front-end circuitry 825 is omitted in favor of thepower amplifier 823 providing the amplified RF signal directly to theantenna 826.

The directional coupler 824 senses an output signal of the poweramplifier 823. Additionally, the sensed output signal from thedirectional coupler 824 is provided to the mixer 838, which multipliesthe sensed output signal by a reference signal of a controlledfrequency. The mixer 838 operates to generate a downshifted signal bydownshifting the sensed output signal's frequency content. Thedownshifted signal can be provided to the ADC 839, which can convert thedownshifted signal to a digital format suitable for processing by thebaseband processor 821. Including a feedback path from the output of thepower amplifier 823 to the baseband processor 821 can provide a numberof advantages. For example, implementing the baseband processor 821 inthis manner can aid in providing power control, compensating fortransmitter impairments, and/or in performing digital pre-distortion(DPD). Although one example of a sensing path for a power amplifier isshown, other implementations are possible.

The PA supply control circuit 828 receives a power control signal fromthe baseband processor 821, and controls supply voltages of the poweramplifier 823. In the illustrated configuration, the PA supply controlcircuit 828 generates a first supply voltage V_(CC1) for powering aninput stage of the power amplifier 823 and a second supply voltageV_(CC2) for powering an output stage of the power amplifier 823. The PAsupply control circuit 828 can control the voltage level of the firstsupply voltage V_(CC1) and/or the second supply voltage V_(CC2) toenhance the power amplifier system's PAE.

The PA supply control circuit 828 can employ various power managementtechniques to change the voltage level of one or more of the supplyvoltages over time to improve the power amplifier's power addedefficiency (PAE), thereby reducing power dissipation.

One technique for improving efficiency of a power amplifier is averagepower tracking (APT), in which a DC-to-DC converter is used to generatea supply voltage for a power amplifier based on the power amplifier'saverage output power. Another technique for improving efficiency of apower amplifier is envelope tracking (ET), in which a supply voltage ofthe power amplifier is controlled in relation to the envelope of the RFsignal. Thus, when a voltage level of the envelope of the RF signalincreases the voltage level of the power amplifier's supply voltage canbe increased. Likewise, when the voltage level of the envelope of the RFsignal decreases the voltage level of the power amplifier's supplyvoltage can be decreased to reduce power consumption.

In certain configurations, the PA supply control circuit 828 is amulti-mode supply control circuit that can operate in multiple supplycontrol modes including an APT mode and an ET mode. For example, thepower control signal from the baseband processor 821 can instruct the PAsupply control circuit 828 to operate in a particular supply controlmode.

As shown in FIG. 8 , the PA bias control circuit 827 receives a biascontrol signal from the baseband processor 821, and generates biascontrol signals for the power amplifier 823. In the illustratedconfiguration, the bias control circuit 827 generates bias controlsignals for both an input stage of the power amplifier 823 and an outputstage of the power amplifier 823. However, other implementations arepossible.

FIG. 9A is a schematic diagram of one embodiment of a packaged module900. FIG. 9B is a schematic diagram of a cross-section of the packagedmodule 900 of FIG. 9A taken along the lines 9B-9B. The packaged module900 can be implemented in accordance with any of the embodiments herein.

The packaged module 900 includes radio frequency components 901, asemiconductor die 902, surface mount devices 903, wirebonds 908, apackage substrate 920, and an encapsulation structure 940. The packagesubstrate 920 includes pads 906 formed from conductors disposed therein.Additionally, the semiconductor die 902 includes pins or pads 904, andthe wirebonds 908 have been used to connect the pads 904 of the die 902to the pads 906 of the package substrate 920.

The semiconductor die 902 includes a power amplifier 945, which can beimplemented in accordance with one or more features disclosed herein.

The packaging substrate 920 can be configured to receive a plurality ofcomponents such as radio frequency components 901, the semiconductor die902 and the surface mount devices 903, which can include, for example,surface mount capacitors and/or inductors. In one implementation, theradio frequency components 901 include integrated passive devices(IPDs).

As shown in FIG. 9B, the packaged module 900 is shown to include aplurality of contact pads 932 disposed on the side of the packagedmodule 900 opposite the side used to mount the semiconductor die 902.Configuring the packaged module 900 in this manner can aid in connectingthe packaged module 900 to a circuit board, such as a phone board of amobile device. The example contact pads 932 can be configured to provideradio frequency signals, bias signals, and/or power (for example, apower supply voltage and ground) to the semiconductor die 902 and/orother components. As shown in FIG. 9B, the electrical connectionsbetween the contact pads 932 and the semiconductor die 902 can befacilitated by connections 933 through the package substrate 920. Theconnections 933 can represent electrical paths formed through thepackage substrate 920, such as connections associated with vias andconductors of a multilayer laminated package substrate.

In some embodiments, the packaged module 900 can also include one ormore packaging structures to, for example, provide protection and/orfacilitate handling. Such a packaging structure can include overmold orencapsulation structure 940 formed over the packaging substrate 920 andthe components and die(s) disposed thereon.

It will be understood that although the packaged module 900 is describedin the context of electrical connections based on wirebonds, one or morefeatures of the present disclosure can also be implemented in otherpackaging configurations, including, for example, flip-chipconfigurations.

FIG. 10A is a schematic diagram of a cross-section of another embodimentof a packaged module 950. The packaged module 950 includes a laminatedpackage substrate 951 and a flip-chip die 952. The packaged module 950can be implemented in accordance with any of the embodiments herein.

The laminated package substrate 951 includes a cavity-based antenna 958associated with an air cavity 960, a first conductor 961, a secondconductor 962. The laminated package substrate 951 further includes aplanar antenna 959.

In certain implementations herein, a packaged module includes one ormore integrated antennas. For example, the packaged module 950 of FIG.10A includes the cavity-based antenna 958 and the planar antenna 959. Byincluding antennas facing in multiple directions (including, but notlimited to, directions that are substantially perpendicular to oneanother), a range of available angles for communications can beincreased. Although one example of a packaged module with integratedantennas is shown, the teachings herein are applicable to modulesimplemented in a wide variety of ways.

FIG. 10B is a perspective view of another embodiment of a packagedmodule 1020. The module 1020 includes a laminated substrate 1010 and asemiconductor die 1012. The semiconductor die 1012 includes at least oneof a front end system 945 or a transceiver 946. For example, the frontend system 945 can include signal conditioning circuits, such ascontrollable amplifiers and/or controllable phase shifters, to aid inproviding beamforming. The packaged module 1020 can be implemented inaccordance with any of the embodiments herein.

In the illustrated the embodiment, cavity-based antennas 1011 a-1011 phave been formed on an edge 1022 of the laminated substrate 1010. Inthis example, sixteen cavity-based antennas have been provided in afour-by-four (4×4) array. However, more or fewer antennas can beincluded and/or antennas can be arrayed in other patterns.

In another embodiment, the laminated substrate 1010 further includeanother antenna array (for example, a patch antenna array) formed on asecond major surface of the laminated substrate 1010 opposite the firstmajor surface 1021. Implementing the module 1020 aids in increasing arange of angles over which the module 1020 can communicate.

The module 1020 illustrates another embodiment of a module including anarray of antennas that are controllable to provide beamforming.Implementing an array of antennas on a side of module aids incommunicating at certain angles and/or directions that may otherwise beunavailable due to environmental blockage. Although an example withcavity-based antennas is shown, the teachings herein are applicable toimplementations using other types of antennas.

FIG. 11 is a schematic diagram of one embodiment of a communicationsystem 1130 for transmitting RF signals. The communication system 1130includes a battery 1101, an envelope tracker 1102, a baseband processor1107, a signal delay circuit 1108, a digital pre-distortion (DPD)circuit 1109, an I/Q modulator 1110, an observation receiver 1111, anintermodulation detection circuit 1112, a power amplifier 1113, adirectional coupler 1114, a duplexing and switching circuit 1115, anantenna 1116, an envelope delay circuit 1121, a coordinate rotationdigital computation (CORDIC) circuit 1122, a shaping circuit 1123, adigital-to-analog converter 1124, and a reconstruction filter 1125. Thecommunication system 1130 can be implemented in accordance with any ofthe embodiments herein.

The communication system 1130 of FIG. 11 illustrates one example of anRF system operating with a power amplifier supply voltage controlledusing envelope tracking. However, envelope tracking systems can beimplemented in a wide variety of ways.

The baseband processor 1107 operates to generate an I signal and a Qsignal, which correspond to signal components of a sinusoidal wave orsignal of a desired amplitude, frequency, and phase. For example, the Isignal can be used to represent an in-phase component of the sinusoidalwave and the Q signal can be used to represent a quadrature-phasecomponent of the sinusoidal wave, which can be an equivalentrepresentation of the sinusoidal wave. In certain implementations, the Iand Q signals are provided to the I/Q modulator 1110 in a digitalformat. The baseband processor 1107 can be any suitable processorconfigured to process a baseband signal. For instance, the basebandprocessor 1107 can include a digital signal processor, a microprocessor,a programmable core, or any combination thereof.

The signal delay circuit 1108 provides adjustable delay to the I and Qsignals to aid in controlling relative alignment between the envelopesignal and the RF signal RF_(IN). The amount of delay provided by thesignal delay circuit 1108 is controlled based on amount ofintermodulation detected by the intermodulation detection circuit 1112.

The DPD circuit 1109 operates to provide digital shaping to the delayedI and Q signals from the signal delay circuit 1108 to generate digitallypre-distorted I and Q signals. In the illustrated embodiment, thepre-distortion provided by the DPD circuit 1109 is controlled based onamount of intermodulation detected by the intermodulation detectioncircuit 1112. The DPD circuit 1109 serves to reduce a distortion of thepower amplifier 1113 and/or to increase the efficiency of the poweramplifier 1113.

The I/Q modulator 1110 receives the digitally pre-distorted I and Qsignals, which are processed to generate an RF signal RF_(IN). Forexample, the I/Q modulator 1110 can include DACs configured to convertthe digitally pre-distorted I and Q signals into an analog format,mixers for upconverting the analog I and Q signals to radio frequency,and a signal combiner for combining the upconverted I and Q signals intoan RF signal suitable for amplification by the power amplifier 1113. Incertain implementations, the I/Q modulator 1110 can include one or morefilters configured to filter frequency content of signals processedtherein.

The envelope delay circuit 1121 delays the I and Q signals from thebaseband processor 1107. Additionally, the CORDIC circuit 1122 processesthe delayed I and Q signals to generate a digital envelope signalrepresenting an envelope of the RF signal RF_(IN). Although FIG. 11illustrates an implementation using the CORDIC circuit 1122, an envelopesignal can be obtained in other ways.

The shaping circuit 1123 operates to shape the digital envelope signalto enhance the performance of the communication system 1130. In certainimplementations, the shaping circuit 1123 includes a shaping table thatmaps each level of the digital envelope signal to a corresponding shapedenvelope signal level. Envelope shaping can aid in controllinglinearity, distortion, and/or efficiency of the power amplifier 1113.

In the illustrated embodiment, the shaped envelope signal is a digitalsignal that is converted by the DAC 1124 to an analog envelope signal.Additionally, the analog envelope signal is filtered by thereconstruction filter 1125 to generate an envelope signal suitable foruse by the envelope tracker 1102. In certain implementations, thereconstruction filter 1125 includes a low pass filter.

With continuing reference to FIG. 11 , the envelope tracker 1102receives the envelope signal from the reconstruction filter 1125 and abattery voltage V_(BATT) from the battery 1101, and uses the envelopesignal to generate a power amplifier supply voltage V_(CC_PA) for thepower amplifier 1113 that changes in relation to the envelope of the RFsignal RF_(IN). The power amplifier 1113 receives the RF signal RF_(IN)from the I/Q modulator 1110, and provides an amplified RF signalRF_(OUT) to the antenna 1116 through the duplexing and switching circuit1115, in this example.

The directional coupler 1114 is positioned between the output of thepower amplifier 1113 and the input of the duplexing and switchingcircuit 1115, thereby allowing a measurement of output power of thepower amplifier 1113 that does not include insertion loss of theduplexing and switching circuit 1115. The sensed output signal from thedirectional coupler 1114 is provided to the observation receiver 1111,which can include mixers for down converting I and Q signal componentsof the sensed output signal, and DACs for generating I and Q observationsignals from the downconverted signals.

The intermodulation detection circuit 1112 determines an intermodulationproduct between the I and Q observation signals and the I and Q signalsfrom the baseband processor 1107. Additionally, the intermodulationdetection circuit 1112 controls the pre-distortion provided by the DPDcircuit 1109 and/or a delay of the signal delay circuit 1108 to controlrelative alignment between the envelope signal and the RF signalRF_(IN).

By including a feedback path from the output of the power amplifier 1113and baseband, the I and Q signals can be dynamically adjusted tooptimize the operation of the communication system 1130. For example,configuring the communication system 1130 in this manner can aid inproviding power control, compensating for transmitter impairments,and/or in performing DPD.

Although illustrated as a single stage, the power amplifier 1113 caninclude one or more stages. Furthermore, the teachings herein areapplicable to communication systems including multiple power amplifiers.In such implementations, separate envelope trackers can be provided fordifferent power amplifiers and/or one or more shared envelope trackerscan be used.

FIGS. 12A and 12B show two examples of power amplifier supply voltageversus time.

In FIG. 12A, a graph 1147 illustrates one example of the voltage of anRF signal 1141 and a power amplifier supply voltage 1143 versus time.The RF signal 1141 has an envelope 1142.

It can be important that the power amplifier supply voltage 1143 of apower amplifier has a voltage greater than that of the RF signal 1141.For example, powering a power amplifier using a power amplifier supplyvoltage that has a magnitude less than that of the RF signal can clipthe RF signal, thereby creating signal distortion and/or other problems.Thus, it can be important the power amplifier supply voltage 1143 begreater than that of the envelope 1142. However, it can be desirable toreduce a difference in voltage between the power amplifier supplyvoltage 1143 and the envelope 1142 of the RF signal 1141, as the areabetween the power amplifier supply voltage 1143 and the envelope 1142can represent lost energy, which can reduce battery life and increaseheat generated in a wireless device.

In FIG. 12B, a graph 1148 illustrates another example of the voltage ofan RF signal 1141 and a power amplifier supply voltage 1144 versus time.In contrast to the power amplifier supply voltage 1143 of FIG. 12A, thepower amplifier supply voltage 1144 of FIG. 12B changes in relation tothe envelope 1142 of the RF signal 1141. The area between the poweramplifier supply voltage 1144 and the envelope 1142 in FIG. 12B is lessthan the area between the power amplifier supply voltage 1143 and theenvelope 1142 in FIG. 12A, and thus the graph 1148 of FIG. 12B can beassociated with a power amplifier system having greater energyefficiency.

FIG. 13A is one example of a graph of current versus time. FIG. 13B isanother example of a graph of current versus time. FIG. 13C is oneexample of a graph of transistor bias source impedance versus frequency.

With reference to FIGS. 13A-13C, the graphs corresponds to simulationsof one implementation of a class E power amplifier operating withadvanced driver gain shaping implemented with 140 MHz (speed 7 ns). InFIG. 13A, power amplifier current is shown when ramping I_(ADS) from 5μA to 170 μA, while FIG. 13B depicts power amplifier current whenramping I_(ADS) from 170 μA to 5 μA. Additionally, FIG. 13C depicts biassource impedance of the driver stage of the class E power amplifier. Theclass E power amplifier provides amplification to an RF signal in Band 8and operates with V_(CC) between 1 V and 5.5 V, in this example.

In this example, the envelope tracker includes a multi-level supply(MLS) envelope tracking system operating with a bandwidth of about 7MHz. As skilled artisans will appreciate, an MLS envelope trackingsystem includes a DC-to-DC converter that generates multiple regulatedvoltages of different voltage levels, and a modulator that controls thesupply voltage of a power amplifier by controlling selection of theregulated voltages over time based on the envelope signal.

FIG. 14A is one example of a graph of amplitude distortion versus outputpower for various implementations of class E power amplifiers. FIG. 14Bis one example of a graph of driver stage base voltage versus outputpower for various implementations of class E power amplifiers. FIG. 14Cis one example of a graph of output stage base voltage versus outputpower for various implementations of class E power amplifiers. FIG. 14Dis one example of current versus frequency for various implementationsof class E power amplifiers.

With reference to FIGS. 14A-14D, the simulations correspond to oneexample of simulation results for a class E power amplifier with gainshaping relative to a class E power amplifier without gain shaping. Theclass E power amplifier operates with a supply voltage of 3V andamplifies an RF signal in Band 8, in this example.

In the illustrated example, at an output power (Pout) of about 25 dBm,the gain of bipolar transistor Q1 starts to expand and the base voltagestarts to increase (Q1 gain shaping start). Additionally, at Pout ofabout 27.5 dBm, bipolar transistor Q2 gain starts to compress and basevoltage start to decrease. In this example, Q1 gain shaping startsbefore Q2 starts to compress. Thus, it would be too late to couple Q2base voltage and drive Q1 bias for Q1 gain shaping.

FIG. 15A is one example of a graph of normalized amplitude distortionversus output power for a class E power amplifier operating at varioussupply voltage levels. FIG. 15B is one example of a graph of normalizedphase distortion versus output power for a class E power amplifieroperating at various supply voltage levels.

With reference to FIGS. 15A-15B, the simulations correspond to oneexample of simulation results for a class E power amplifier without gainshaping. The class E power amplifier operates with a supply voltagevarying from 1 V to 5.5 V and amplifies an RF signal in Band 8, in thisexample.

FIG. 16A is another example of a graph of normalized amplitudedistortion versus output power for a class E power amplifier operatingat various supply voltage levels. FIG. 16B is another example of a graphof normalized phase distortion versus output power for a class E poweramplifier operating at various supply voltage levels.

The simulations of FIGS. 16A and 16B correspond to one example ofsimulation results for a class E power amplifier with advanced gainshaping. The class E power amplifier operates with a supply voltagevarying from 1 V to 5.5 V and amplifies an RF signal in Band 8, in thisexample.

With reference to FIGS. 15A-16B, both amplitude distortion (AM/AM) andphase distortion (AM/PM) are improved by using advanced gain shaping.Furthermore, higher VCC gain expansion is provided to improve linearity.Additionally, a flatter landing zone is provided at low VCC, and lessgain expansion is provided at high VCC. Thus, gain expansion table foreach VCC can be selected depending on the linearity margin.

FIG. 17A is one example of measurement results of gain versus outputpower for a class E power amplifier operating at various supply voltagelevels. FIG. 17B is another example of measurement results of gainversus output power for a class E power amplifier operating at varioussupply voltage levels. The measurement results correspond to a oneimplementation of a class E power amplifier with advanced gain shaping.

With reference to FIGS. 17A and 17B, the measurements results depictsimilar characteristics as the simulation results.

Applications

The principles and advantages of the embodiments described herein can beused for a wide variety of applications.

For example, power amplifier systems can be included in a wide range ofradio frequency electronics including, but not limited to, a basestation, a wireless network access point, a mobile phone (for instance,a smartphone), a tablet, a vehicle, a computer, and/or an Internet ofthings (IoT) device.

CONCLUSIONS

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Likewise, the word “connected”, as generally used herein, refers to twoor more elements that may be either directly connected, or connected byway of one or more intermediate elements. Additionally, the words“herein,” “above,” “below,” and words of similar import, when used inthis application, shall refer to this application as a whole and not toany particular portions of this application. Where the context permits,words in the above Detailed Description using the singular or pluralnumber may also include the plural or singular number respectively. Theword “or” in reference to a list of two or more items, that word coversall of the following interpretations of the word: any of the items inthe list, all of the items in the list, and any combination of the itemsin the list.

Moreover, conditional language used herein, such as, among others,“may,” “could,” “might,” “can,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/orstates are included or are to be performed in any particular embodiment.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A power amplifier system comprising: a poweramplifier configured to amplify a radio frequency signal and to receivepower from a supply voltage; an envelope tracker configured to control avoltage level of the supply voltage of the power amplifier based on anenvelope of the radio frequency signal; a current controller configuredto receive power from the supply voltage and to generate a gain shapingcurrent that changes based on the voltage level of the supply voltage,the current controller further configured to generate a referencecurrent; and a power amplifier biasing circuit configured to bias thepower amplifier based on combining the reference current and the gainshaping current.
 2. The power amplifier system of claim 1 wherein thecurrent controller includes a look-up table mapping the voltage level ofthe supply voltage to the gain shaping current.
 3. The power amplifiersystem of claim 1 wherein the current controller reduces the gainshaping current in response to an increase in the voltage level of thesupply voltage.
 4. The power amplifier system of claim 1 wherein thecurrent controller includes a plurality of current steering circuitseach configured to control the gain shaping current.
 5. The poweramplifier system of claim 4 wherein the current controller includes aregulator configured to generate a plurality of reference voltages ofdifferent voltage levels, the plurality of current steering circuitseach configured to compare the supply voltage to a corresponding one ofthe plurality of reference voltages.
 6. The power amplifier system ofclaim 4 wherein the current controller includes a regulator configuredto generate a common reference voltage and a resistor ladder configuredto receive the supply voltage and to generate a plurality of scaledsupply voltages, the plurality of current steering circuits eachconfigured to compare the common reference voltage to a correspondingone of the plurality of scaled supply voltages.
 7. The power amplifiersystem of claim 1 wherein the power amplifier biasing circuit biases adriver stage of the power amplifier.
 8. The power amplifier system ofclaim 1 wherein the power amplifier biasing circuit is configured toprovide a bias signal to the power amplifier at a bias output, the poweramplifier biasing circuit including a power control circuit configuredto control the bias signal based on a plurality of power controlsignals.
 9. The power amplifier system of claim 8 further comprising aninput matching network connected between an input terminal and an inputto the power amplifier, the power amplifier biasing circuit furtherincluding a capacitor configured to couple a portion of the radiofrequency signal at the input terminal to the bias output.
 10. A methodof amplification in a mobile device, the method comprising: amplifying aradio frequency signal using a power amplifier that is powered by asupply voltage; controlling a voltage level of the supply voltage of thepower amplifier based on an envelope of the radio frequency signal usingan envelope tracker; generating a gain shaping current that changesbased on the voltage level of the supply voltage and generating areference current using a current controller that is powered by thesupply voltage; and biasing the power amplifier based on combining thereference current and the gain shaping current using a power amplifierbiasing circuit.
 11. The method of claim 10 further comprising mappingthe voltage level of the supply voltage to the gain shaping currentusing a look-up table of the current controller.
 12. The method of claim10 further comprising reducing the gain shaping current in response toan increase in the voltage level of the supply voltage of the poweramplifier.
 13. The method of claim 10 wherein biasing the poweramplifier includes biasing a driver stage of the power amplifier.
 14. Amobile device comprising: a power management system including anenvelope tracker configured to control a voltage level of a supplyvoltage based on an envelope of a radio frequency signal; a transceiverconfigured to generate the radio frequency signal; and a front endsystem including a power amplifier configured to amplify the radiofrequency signal and to receive power from the supply voltage, and acurrent controller configured to receive power from the supply voltageand to generate a gain shaping current that changes based on the voltagelevel of the supply voltage, the current controller further configuredto generate a reference current, the front end system further includinga power amplifier biasing circuit configured to bias the power amplifierbased on combining the reference current and the gain shaping current.15. The mobile device of claim 14 wherein the current controllerincludes a look-up table mapping the voltage level of the supply voltageto the gain shaping current.
 16. The mobile device of claim 14 whereinthe current controller reduces the gain shaping current in response toan increase in the voltage level of the supply voltage.
 17. The mobiledevice of claim 14 wherein the current controller includes a pluralityof current steering circuits each configured to control the gain shapingcurrent.
 18. The mobile device of claim 14 wherein the power amplifierbiasing circuit biases a driver stage of the power amplifier.
 19. Themobile device of claim 14 wherein the power amplifier biasing circuit isconfigured to provide a bias signal to the power amplifier at a biasoutput, the power amplifier biasing circuit including a power controlcircuit configured to control the bias signal based on a plurality ofpower control signals.
 20. The mobile device of claim 19 wherein thefront end system further includes an input matching network connectedbetween an input terminal and an input to the power amplifier, the poweramplifier biasing circuit further including a capacitor configured tocouple a portion of the radio frequency signal at the input terminal tothe bias output.